Work and leisure are opposites inextricably entangled with each other, like yin and yang. In economics, the distinction has been formalized in a variety of ways. One distinction focuses on market work, and proposes that work is a disutility (a bad thing, an annoyance) that people have to be paid to do. Leisure, on the other hand, is a utility (a good thing) that people have to be paid to abandon. (See, e.g., Gratton & Taylor, “The Economics of Work and Leisure,” 2004.)
However, not all time outside of market work is truly leisure: there’s a big difference between washing the dishes and watching television. An alternative economic approach is to distinguish work and leisure by the degree to which they can be substituted with market inputs: work is something for which market substitutes exist (Aguiar and Hurst, “Measuring Trends in Leisure: The Allocation of Time over Five Decades,” 2006). For instance, the work of cooking can be substituted with restaurants, prepared meals, microwaves, and the like. Watching television is leisure, by this definition, because one “cannot use the market to reduce the time input into watching television (ibid.).” In this approach, “the leisure content of an activity is a function of technology rather than preferences.” It doesn’t matter if you enjoy cooking or not; it counts as work because there is a market substitute.
A synthesis of these might define work as a disutility for which one must be compensated, OR for which one would have to compensate others to do.
Consider an alternative definition by Robert E. P. Levy:
Any human activity or feature of human activity undertaken as a means to some desired state of affairs can be called work, and thus any kind of play is pervasively laden with elements of productive work
Work is different from play only in that the means are valued less than ends
Play is different from work only in that it is already realizing its value by its means, independent of what might come of it.
So clearly there is no dividing line between work and play, just work-like and play-like aspects of human activities.